Systems for Surface Treatment of Semiconductor Substrates using Sequential Chemical Applications

ABSTRACT

Systems for removing post etch polymer residue from etched surface includes a first proximity head to introduce a first cleaning chemistry as a first meniscus to a portion of the surface of the substrate so as to cover a length that extends to at least a diameter of the substrate and a first width that is less than the diameter of the substrate. A second proximity head is configured to introduce a second cleaning chemistry as a second meniscus to the portion so as to cover the length that extends to the diameter and a second width that is less than the diameter of the substrate. A substrate supporting device equipped with a motor coupled to a computing system is used to move the substrate supporting device under the first proximity head at a first linear speed and under the second proximity head at a second linear speed.

CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. §120 as a divisionalapplication to co-pending U.S. patent application Ser. No. 12/212,559,filed Sep. 17, 2008, entitled “Method and Apparatus for SurfaceTreatment of Semiconductor Substrates using Sequential ChemicalApplications,” which claims priority under 35 U.S.C. 119(e) to U.S.Provisional application No. 61/083,498, filed on Jul. 24, 2008, andentitled “Method and Apparatus for Surface Treatment of SemiconductorSubstrates using Sequential Chemical Applications,” contents of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor substrateprocessing, and more particularly, to systems and methods for treating asurface of a semiconductor substrate using sequential chemicalapplications.

DESCRIPTION OF THE RELATED ART

Semiconductor devices are obtained through various fabricationoperations. The fabrication operations define a plurality of features,such as gate structures, on semiconductor wafers (wafers or substrates)that span multi-levels. During the various fabrication operations, thesubstrate is exposed to various contaminants. Any material or chemicalused in the fabrication operations to which the substrate is exposed isa potential source of contamination. Chemicals used in the variousfabrication operations, such as etching, deposition, etc., leavedeposit, such as process gases, etching chemicals, deposition chemicals,etc., on and around features, such as gate structures, formed on thesurface of the substrate, as particulates or polymer residuecontaminants. The sizes of the particulate contaminants are in the orderof the critical dimensions of the features being fabricated on thesubstrate. These contaminants lodge on the top, along the side walls andin between the features in hard-to-reach areas, such as in a trenchsurrounding the delicate features, and may likely cause damage to thefeatures within the vicinity of the contaminant particles.

A typical gate structure formed on a substrate may include a stack oflayers made of different materials defining the gate structure. The gatestructure may include a layer of gate oxide over which an electrode isfabricated using one or more layers of metal, such as tungsten, tungstencompounds, etc. The metal that may be used in fabricating the electrodemay include tungsten, tungsten silicide, tungsten nitride, tantalum,polysilicon, silicon oxide, aluminum oxide, hafnium oxide, siliconoxynitride, tantalum nitride, etc. A layer of polysilicon is formed ontop of the metal layer and a hardmask layer is fabricated over the topof the polysilicon layer. The hardmask layer is fabricated as aphotoresist layer and is used to pattern the gate stack and preserve theunderlying layers. During an etching operation, etching chemicals usedin patterning the hardmask and the underlying layers leave polymerresidue on top and along the sidewalls of the gate structure.Conventional polymer residue cleaning methods have relied on batch toolsthat expose the polymer residues to cleaning chemistries for a prolongedperiod of time. When a less aggressive cleaning chemistry is used, theexposure results in inefficient removal of polymer residues and othercontaminants. On the other hand, when a more aggressive chemistry isused, the exposure using the batch tools leads to high material lossrates at the gate structure rendering the cleaning process undesirable.The material loss includes pullback of the hardmask layer and/orundercut of gate oxide and other layers of the gate structure formed onthe substrate. FIG. 1 illustrates a typical gate structure and FIG. 2illustrates an example of some of the negative effects experienced atvarious layers of the gate structure.

FIG. 1 illustrates a typical metal gate structure formed on a substrate100 by various fabrication operations. An etching operation is used toform various layers of the gate structure thereby defining a gate stack.The gate structure includes a layer of gate oxide 115 formed on thesubstrate 100. The substrate 100 includes a source/drain region 105 overwhich the layer of gate oxide 115 (usually of high dielectric constant)is formed. A metal electrode is fabricated over the gate oxide 115 usingone or more layers of metal. In the metal gate structure illustrated inFIG. 1, the metal electrode is formed using a layer of metal 1 120 and alayer of metal 2 122. A polysilicon layer 125 is formed over the metallayer and a hardmask layer is formed over the polysilicon layer. Thehardmask layer may further include one or more layers of hardmask. Asdepicted in FIG. 1, the hardmask layer includes 3 layers of hardmask,mask 1 130, mask 2 132, and mask 3 134. The etched materials and theetching chemicals used in the etching operation to define the stackdeposit metallic or polymer contaminants on the top and sidewalls of thegate structure. Typical contaminants include polymer residues 140 andmetal containing polymer residues 142.

FIG. 2 illustrates some of the potential issues experienced at the gatestructure as a result of a cleaning process using a traditional batchtool. The prolonged exposure of the gate structure to aggressivecleaning chemistry used in the batch tool results in the erosion of thehardmask, otherwise known as hardmask pullback. The hardmask erosionresults in the premature exposure of the underlying layers leading topotential damage and/or further contamination of the gate features. Theprolonged exposure to the cleaning chemistry may further result in theundercut of the metal layer, such as tungsten, tungsten silicide, etc.,used in forming the metal electrode over the gate oxide eventuallyexposing the gate oxide to the cleaning chemistry. The pullback of thehardmask and the undercut of the metal and other layers of the gatestructure including the gate oxide pose the greatest problems in thecleaning process. The premature exposure of the various layers of a gatestack to chemistries used in subsequent fabrication operations mayresult in further damage of the layers lending the gate structureinoperable. Efficient and non-damaging removal of contaminants duringfabrication poses a great challenge in the cleaning process.

In view of the foregoing, a more effective cleaning technology is neededin removing the contaminants from the surface of the substrate whilepreserving the structural integrity of the gate structure. It is in thiscontext embodiments of the invention arise.

SUMMARY

The present invention fills the need by providing improved methods andapparatus for efficiently removing polymer residue contaminants formedaround a metal gate structure on the surface of the substrate. It shouldbe appreciated that the present invention can be implemented in numerousways, including an apparatus and a method. Several inventive embodimentsof the present invention are described below.

In one embodiment, a system for preparing a surface of a substrate byremoving post etch polymer residue from etched surfaces that define agate structure formed from at least one layer of tungsten metal, isdefined. The system includes a first proximity head configured tointroduce a first cleaning chemistry as a first meniscus to a portion ofthe surface of the substrate, when present. The first proximity head isdesigned to cover a length that extends to at least a diameter of thesubstrate and a first width that is less than the diameter of thesubstrate, when present. The system includes a second proximity headconfigured to introduce a second cleaning chemistry to the portion ofthe surface of the substrate as a second meniscus. The second proximityhead is designed to cover a length that extends to at least a diameterof the substrate and a second width that is less than the diameter ofthe substrate, when present. The first and second cleaning chemistriesare introduced sequentially. The system also includes a substratesupporting device to receive and transport the substrate. The substratesupporting device is equipped with a motor that is coupled to acomputing system to control movement of the substrate supporting deviceto, (a) move under the first proximity head at a first linear speed soas to expose the portion of the surface of the substrate to the firstcleaning chemistry for a pre-defined exposure time, and (b) move underthe second proximity head at a second linear speed.

In another embodiment, a system for preparing a surface of a substrateby removing post etch polymer residue from etched surfaces that define agate structure formed from at least one layer of tungsten metal, isdisclosed. The system includes a first proximity head configured tointroduce a first cleaning chemistry as a first meniscus to a portion ofthe surface of the substrate, when present. The first proximity head isdesigned to introduce the first meniscus to cover a length that extendsto at least a diameter of the substrate and a first width that is lessthan the diameter of the substrate, when present. The system includes asecond proximity head configured to introduce a second cleaningchemistry to the portion of the surface of the substrate as a secondmeniscus. The second proximity head is designed to introduce the secondmeniscus to cover the length that extends to at least the diameter ofthe substrate and a second width that is less than the diameter of thesubstrate, when present. The first and second cleaning chemistries areintroduced sequentially. The system also includes a substrate supportingdevice to receive and transport the substrate, when present. Thesubstrate supporting device includes a motor that is coupled to acomputing system to control movement of the substrate supporting deviceto, (a) move under the first proximity head at a first linear speed soas to expose the portion of the surface of the substrate, when present,to the first cleaning chemistry for a first pre-defined exposure time,wherein the first pre-defined exposure time is defined by the firstlinear speed and the first width of the first meniscus, and (b) moveunder the second proximity head at a second linear speed so as to exposethe portion of the surface of the substrate to the second cleaningchemistry for a second pre-defined exposure time, wherein the secondpre-defined exposure time is defined by the second linear speed and thesecond width of the second meniscus.

In yet another embodiment, a system for removing post etch polymerresidue from etched surfaces that define a metal gate structure formedfrom at least one layer of tungsten metal, is disclosed. The systemincludes a carrier, a first proximity head, a second proximity head anda motor. The carrier is configured to receive and transport thesubstrate. The first proximity head is configured to introduce a firstcleaning chemistry to a portion of the surface of the substrate as afirst meniscus. The second proximity head is configured to introduce asecond cleaning chemistry to the portion of the surface of the substrateas a second meniscus. The first and the second cleaning chemistries areintroduced sequentially. The motor is configured to move the carrierunder the first and the second proximity heads to enable application ofthe first and the second cleaning chemistries to the portion of thesurface of the substrate. The motor is coupled to a computing system tocontrol a linear speed of the carrier moving under the first proximityhead and the secondary proximity head so as to expose the portion of thesubstrate to the first and the second cleaning chemistries for anexposure time defined by the linear speed.

Other aspects and advantages of the invention will become more apparentfrom the following detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings. Thesedrawings should not be taken to limit the invention to the preferredembodiments, but are for explanation and understanding only.

FIG. 1 illustrates a simplified schematic diagram of a typical post-etchmetal gate structure, in one embodiment of the invention.

FIG. 2 illustrates a simplified schematic diagram of potential issuesand damages experienced at the post-etch metal gate structureillustrated in FIG. 1 during cleaning operation, in one embodiment ofthe invention.

FIGS. 3A-3D illustrate simplified schematic diagrams of various gatestructures after etching operation. FIG. 3A illustrates a simplifiedDRAM gate structure after full etch, in one embodiment of the invention.FIG. 3B illustrates a simplified DRAM gate structure after partial etch,in another embodiment of the invention. FIG. 3C illustrates a simplifiedFlash tungsten gate structure after an etching operation, in anotherembodiment of the invention. FIG. 3D illustrates a simplified tungstengate Logic structure after an etching operation, in another embodimentof the invention.

FIG. 3E illustrates a simplified schematic diagram of a tungsten metalgate structure after a typical tank cleaning operation, in oneembodiment of the invention.

FIGS. 4A-4C illustrate simplified schematic diagrams of desired cleaningresults expected for various gate structures illustrated in FIGS. 3A-3Cafter a cleaning operation.

FIG. 4D illustrates a resultant metal gate structure after a cleaningoperation using a first cleaning chemistry and second cleaningchemistry, in one embodiment of the invention.

FIG. 5 illustrates a simplified schematic diagram of a system used inthe application of first and second application chemistry to the surfaceof the substrate, in one embodiment of the invention.

FIGS. 6A and 6B illustrate graphs identifying effective removal rate ofpolymer residue using the first and second cleaning chemistry, in oneembodiment of the invention.

FIG. 7 illustrates the optimal exposure time and carrier speed requiredfor effective removal of metal containing polymer residue removal, inone embodiment of the invention.

FIG. 8 illustrates the optimum concentration for effective metalcontaining polymer residue removal rate, in one embodiment of theinvention.

FIG. 9 illustrates various method operations involved in removingpolymer residue from around a metal gate structure during post-etchcleaning operation, in one embodiment of the invention.

DETAILED DESCRIPTION

Several embodiments for effectively removing polymer residues, includingmetal containing polymer residues, from around a metal gate structureformed on a surface of a substrate will now be described. It will beobvious, however, to one skilled in the art, that the present inventionmay be practiced without some or all of these specific details. In otherinstances, well known process operations have not been described indetail in order not to unnecessarily obscure the present invention.

Effective removal of contaminants, such as polymer residues and metalcontaining polymer residues, from the surface of a substrate helps inretaining the functionality of the features formed on the substrate andthe resulting devices, such as microchips. In one embodiment of theinvention, the polymer residues formed around a metal gate structure areremoved by sequentially applying aggressive chemistries to the surfaceof the substrate. The aggressive chemistries are applied in a verycontrolled manner so as to enable optimal removal of the polymer residuecontaminants from around the gate structure while preserving thestructural integrity of the gate structure. In order to apply theaggressive chemistries in a very controlled manner, a plurality ofprocess parameters associated with the gate structure and the polymerresidue are determined. The process parameters are obtained by analyzingthe plurality of fabrication layers forming the gate structure and thevarious types of polymer residues formed around the gate structurefeature. The process parameters define one or more characteristicsassociated with the different layers of the gate structure and thepolymer residue. A first and a second aggressive chemistry areidentified and one or more application parameters are defined for theidentified aggressive chemistries based on the process parameters. Theapplication parameters are used in applying the aggressive chemistriessequentially in a controlled manner so that optimal removal of polymerresidues is enabled without losing the structural integrity of the gatestructure.

The advantages of the various embodiments include use of simple, commonchemistries to effectively remove the unwanted polymer residue resultingin a substantially clean device. The controlled application of theaggressive chemistries effectuates removal of polymer residue withprecise control of critical dimension.

In order to understand the effectiveness of controlled application ofthe aggressive chemistries, the negative effects experienced at the gatestructure will be first described with reference to FIGS. 1 and 2. FIG.1 illustrates a simplified schematic diagram of a gate structure, in oneembodiment of the invention. The gate structure is formed using aplurality of fabrication layers where fabrication materials aredeposited over a surface of a substrate 100. The fabrication layers mayinclude one or more layers of metal 120, 122 formed over a layer of gateoxide 115 on the surface of a substrate 100. The gate oxide layer 115 isusually a high dielectric constant film layer formed over thesource/drain 105. Layers of metals are used to form a metal electrode.In FIG. 1, two layers of metal, Metal 1 120 and Metal 2 122, are used informing the metal electrode. Some of the metals that are used forforming the metal electrode include Tungsten (W), Tungsten Silicide,Tungsten Nitride, Tantalum, poly-silicon (doped or undoped), SiliconOxide (SiO₂) Tantalum Nitride (TaN), Hafnium Oxide, Aluminum Oxide,Nitrided Hafnium-silicate (HfSiON), etc. A polysilicon layer 125 isformed over the metals. A hardmask layer 130 is formed over thepolysilicon layer 130. The hardmask layer 130 may be made up of aplurality of layers of hardmask 130, 132, 134. Typical materials used toform hardmask layers include Silicon Nitride, Silicon Oxide, etc. Thehardmask layer is formed as a photoresist layer and is used to protectthe underlying layers during an etching operation. During the etchingoperation, the etching chemicals used to define the metal gate structurewill leave polymer residue contaminants 140 and metal containing polymerresidue contaminants 142 on top and along the sidewalls of the metalgate structure. It is essential to remove the unwanted polymer residuecontaminants 140, 142 while preserving the characteristics of the metalgate structure.

The gate structure illustrated in FIG. 1 is one example of a gatestructure formed over the substrate. Variations of the gate structureare possible. FIGS. 3A-3D illustrate some variations of the gatestructure illustrated in FIG. 1. FIG. 3A illustrates a DRAM gatestructure after a full etch. A gate stack of the gate structure includesa gate oxide 115 formed over a silicon substrate 100. A poly siliconlayer 125 is formed over the gate oxide 115 followed by a layer of metal1 120 and a layer of metal 2 122. A hardmask layer 130 is formed overthe metal 2 layer. As can be seen, after the etching operation post-etchpolymer residues 140 and metal containing polymer residues 142 formaround the gate structure. It is a challenge to get rid of the polymerresidues formed around the gate structure without actually damaging thevarious layers of the gate structure.

FIG. 3B illustrates a variation of the gate structure shown in FIG. 3A.The gate structure in FIG. 3B is formed as a result of an open etchprocess with the poly silicon layer 125 formed over the entirety of thegate oxide 115 and the gate stack is formed over a portion of the polysilicon layer 125.

FIG. 3C illustrates an embodiment of a flash tungsten metal gatestructure formed over the silicon substrate 100. The gate stack of thegate structure includes a gate oxide 115 formed over the substrate. Aprotective layer of silicon nitride 152 is formed over the gate oxide115. Layers of metal 1, 120, metal 2, 122 and metal 3, 124, are formedon top of the silicon nitride layer 152. A hardmask layer 130 is formedon top of the metal layer 124.

FIG. 3D illustrates a post-etch gate structure formed over the siliconsubstrate 100, in one embodiment of the invention. As mentioned earlierwith other gate structures, a high dielectric constant film layer 115 isformed over the silicon substrate, a plurality of metal layers, such asa layer of metal 2, 122, and metal 1, 120, are formed over the highdielectric constant film layer 115. The metal layers may be tungsten ortantalum based metal layers, such as tungsten, tungsten silicide,tantalum, tantalum nitride, etc. On top of the metal layers, a layer ofpoly silicon 125 is formed. On top of the poly silicon 125, a hardmasklayer is formed. The various chemicals used in the etching operationdeposit around the gate features as polymer residues 140. Removal of thepost-etch polymer residues 140 including metal containing polymerresidues 142 are challenging as the chemicals used to remove theseresidues during a cleaning operation, tend to damage one or more layersof the gate structure. FIG. 2 illustrates one such example of potentialcleaning issues of mask pullback and undercut to the metal layers due tometal corrosion, when the traditional cleaning tools were used.

FIG. 3E illustrates another potential cleaning issue when a batch toolis used during cleaning operation. A batch tool, such as an immersiontank tool, (for example, Process of Record (POR) tank tool, is used toeffectively remove the polymer residue contaminants. The batch toolexposes the substrate with the associated gate structure to the cleaningchemistry for effective removal of the polymer residue. Using a lessaggressive chemistry in the tank tool leads to inefficient cleaningprocess. When a more aggressive chemistry is used in the tank tool, thegate structure experiences high material loss, as illustrated in FIG.3E. The aggressive chemistry used to dissolve the metal containingpolymer residue contaminant will also react with the hardmask layerseverely eroding the hardmask layer thereby exposing the underlyinglayers of the gate structure to the aggressive cleaning chemistriesduring cleaning and post-cleaning process. The exposed layers of thegate structure may undergo severe damage from the aggressive cleaningand other fabrication chemicals resulting in a damaged or inoperablegate structure.

Conventional methods used an immersion tool to expose the surface of thesubstrate to cleaning chemistries. When a less aggressive cleaningchemistry is used in the immersion tool, the cleaning was inefficientwith very poor profile control. On the other hand, when a moreaggressive chemistry is used to treat the surface of the substrate,substantial damage to the fabrication layers occurs including pullbackof the hardmask layer and undercut of the various fabrication layers, asillustrated in FIG. 2. This is due to the fact that the polymer residueson the sidewalls and on top of the gate structure contain metal. Inorder to effectively remove the metal containing polymer residues,aggressive chemistries are chosen such that the aggressive chemistriesare capable of dissolving and/or removing the metal containing polymerresidue during the cleaning operation. These aggressive chemistries,however, also react with the metal containing fabrication layers and thehardmask layers resulting in removing portions of hardmask layers(hardmask pull back) and undercutting portions of the metal containingfabrication layers of the gate structure. When there is a pullback inthe hardmask layer, the underlying fabrication layers that form the gatestructure are prematurely exposed to ambient environment which includeschemicals used in subsequent fabrication operations, leading tocontamination or damage of the underlying layers. Thecontaminated/damaged underlying layers may render the resulting deviceinoperative. It is, therefore, beneficial to prevent the hardmaskpullback while preserving the underlying fabrication layers that mayotherwise prematurely expose the gate oxide layer to fabricationchemicals.

FIGS. 4A-4C illustrate the cleaning results desired from a cleaningoperation for various gate structures depicted in FIGS. 3A-3C. Theexpected desired result preserves the various fabrication layers of thegate structure while effectively removing the polymer residuecontaminants from around the gate structure. Towards this end, FIG. 4Aillustrates the desired result expected after a cleaning operation for afull-etch gate structure illustrated in FIG. 3A, FIG. 4B illustrates thedesired cleaning result for a open-etch gate structure illustrated inFIG. 3B and FIG. 4C illustrates the desired cleaning result for atungsten metal gate structure illustrated in FIG. 3C. As can be seen,the desired results require effective removal of the polymer residuecontaminants, including the metal containing residues, without damagingany of the fabrication layers.

FIG. 5 illustrates a system 500 within a clean room used to introduce afirst cleaning chemistry and a second cleaning chemistry to a surface ofa substrate 100 in a controlled manner to substantially remove polymerresidues deposited around metal gate structures, in one embodiment ofthe invention. The system 500 includes a housing chamber 510 having asubstrate supporting device, such as a carrier 550, to receive, supportand transport a substrate through the housing chamber 510 on a selectedplane. The substrate 100 is received at the substrate input region 515,transported through a region with one or more sets of proximity heads545 and 555 and delivered to the substrate output region 560. Theembodiment of FIG. 5 shows a pair of proximity heads positioned oneither side of the selected plane through which the substrate 100 istransported, to deliver the first and second cleaning chemistries toboth sides of the substrate 100. It should be noted that thisconfiguration of proximity heads is exemplary and should not beconstrued as limiting. As a result, other combinations andconfigurations of proximity heads may also be considered for effectivecleaning of the substrate 100.

The first set of proximity heads 545 are used to apply a first cleaningchemistry and the second set of proximity heads 555 are used to apply asecond cleaning chemistry, respectively, as menisci to the surface ofthe substrate during a post-etch cleaning operation. The term,“meniscus,” as used herein, refers to a volume of liquid bounded andcontained in part by surface tension of the liquid. The meniscus,defining a contained chemical region, is controllable and can be movedover a surface in the contained shape. Furthermore, the meniscus shapecan be controlled through a computing system 505 connected to theproximity heads 545 and 555. The system 510 may include reservoirs 525and 530 to receive, hold and supply the first and second cleaningchemistries to the proximity heads, 545 and 555. A chemistry applicationmechanism 520 connected to the reservoirs 525 and 530 control the flowof the first and second cleaning chemistries through the proximity heads545 and 555. The chemistry application mechanism 520 may include one ormore precision controls to enable controlled delivery of the first andsecond cleaning chemistries to the proximity heads 545 and 555. Theprecision controls may be remotely controlled by the computing system505. Software in the computing system 505 may be used to manipulate theprecision controls such that proper amount of first and secondapplication chemistries are supplied to the proximity heads atappropriate stages of the cleaning process. A plurality of processparameters associated with the various fabrication layers and thepolymer residue contaminants is used to manipulate the delivery controlsso that adequate amounts of the first and second cleaning chemistriesare delivered to the proximity heads.

The application of the first and second cleaning chemistries is based onthe plurality of process parameters. The process parameters are obtainedby analyzing various fabrication layers that form the gate structure andthe polymer residues that need to be removed. The process parametersdefine characteristics of each of the fabrication layers and the polymerresidue. Some of the process parameters associated with each of thefabrication layers at the gate structure include one or more of type,size, and composition. Some of the process parameters associated withthe polymer residue removal may include chemistry type, concentration,temperature, exposure time, and target removal rate on semiconductormaterials used in the process of gate manufacturing. Some of thesemiconductor materials used in the process of gate manufacturing mayinclude Silicon oxide (SiO₂), Tungsten (W), Tungsten silicide, TungstenNitride, Tantalum Nitride, Tantalum, and others. The first cleaningchemistry and second cleaning chemistry are selected based on theprocess parameters so that the polymer residue contaminants areeffectively and substantially removed without damaging the gatestructure feature. The process parameters associated with thefabrication layers and polymer residues may vary from one substrate tothe next. It is essential to preserve the gate structure formed on thesurface of the substrate during the cleaning operation so that thefunctionality of the gate structure and that of the semiconductor deviceis maintained.

The first and second cleaning chemistries that are selected based onprocess parameters are aggressive chemistries that are normally not usedin traditional tools during the cleaning operation. These aggressivechemistries are known to cause considerable damage to the featuresformed on the substrate 100 when exposed over an extended period oftime. However, these aggressive chemistries facilitate effective removalof polymer residues formed around the gate structures when applied in acontrolled manner for a limited amount of time. In one embodiment, thefirst cleaning chemistry is ammonium peroxide mixture (APM) and thesecond cleaning chemistry is diluted Hydrofluoric acid (dHF). APM is aneffective cleaning chemistry as it is known to interact with metalcontaining polymer residues effectively removing them from aroundfeatures formed on the substrate. However, as mentioned earlier, APM isalso known to be an aggressive chemistry with high removal rates fortungsten and tungsten containing compounds making it difficult to use itas an effective cleaning chemistry for cleaning tungsten containingdevice stacks, such as the gate structures, in conventional batchcleaning tools. In order to avoid damage to the fabrication layers ofthe gate structure, especially the ones that contain tungsten/tungstencompounds, the first and second cleaning chemistries are applied in avery controlled manner using the proximity heads 545 and 555,respectively, so as to limit the exposure of the surface of thesubstrate to the cleaning chemistries. The length and precise exposuretime using proximity heads may be driven by a desired target removalrate of the polymer residue so as to enable one to define acceptableamount of metal film loss in the fabrication layers of the featureduring APM application.

To assist in limiting the exposure of the substrate surface to thecleaning chemistries, one or more application parameters are defined foreach of the first and second cleaning chemistries based on the processparameters associated with the various fabrication layers of thefeatures, such as gate structures, and the polymer residue contaminants.Some of the application parameters that may be defined for each of thefirst and second cleaning chemistries may include chemistry type, theorder of application of first and second cleaning chemistry,concentration, exposure time, temperature, pressure, and flow rate. Inone embodiment, exposure time may be further defined as a function oflinear speed at which the substrate is transported under the proximityheads and the width of the meniscus that may be applied to the surfaceof the substrate. Accordingly, F(t_(exposure time))=f (MeniscusWidth/surface area, substrate linear speed). The linear speed of thewafer may be controlled using mechanical devices such as a motor. Forinstance, if the proximity head 545 is capable of applying a meniscusthat is about 20 mm wide, then the linear speed of the substrate may beadjusted to about 20 mm/sec to give an exposure time for the applicationof first cleaning chemistry of 1 second. Depending on the exposure timedesired for each of the first and second cleaning chemistries, thelinear speed of the substrate under the proximity heads may be adjustedaccordingly using the motor.

Upon establishing the application parameters for the cleaningchemistries, the first and second cleaning chemistries are applied tothe surface of the substrate sequentially in a controlled manner usingthe first and second proximity heads, 545 and 555, based on theapplication parameters. The order of the application of the cleaningchemistries is not rigid. In one embodiment, first cleaning chemistry(APM) is applied using the first proximity head 545 followed by theapplication of the second cleaning chemistry (dHF) using the secondproximity head 555. In another embodiment, the first cleaning chemistry(APM) is applied using the second proximity head 555 sequentially afterthe application of the second cleaning chemistry (dHF) using the firstproximity head 545. The order of application of the cleaning chemistriesmight be based on desired outcomes, such as the amount of metal oxide tobe preserved. The controlled sequential application of the first andsecond cleaning chemistries aid in substantial removal of the polymerresidue from around features, such as gate structures, without damagingthe features. As mentioned earlier, the exposure time of each of thecleaning chemistries is controlled by controlling the linear speed ofthe substrate under the corresponding proximity heads.

The application of each of the first and second cleaning chemistries maybe followed by a rinsing operation using a rinsing chemistry. Therinsing chemistry is used to remove any residual cleaning chemistryapplied to the substrate surface after the respective cleaningoperation. Consequently, the order of treatment of various chemistries,in one embodiment of the invention, may include application of firstcleaning chemistry, rinsing operation with a rinsing chemistry,application of second cleaning chemistry and rinsing operation with arinsing chemistry. The rinsing operation following the application ofeach of the first and second cleaning chemistries may use the samerinsing chemistry or different rinsing chemistries.

The first and second proximity heads (545, 555) are configured todeliver the cleaning chemistry and the rinsing chemistry as menisci toclean and rinse the surface of the substrate. The cleaning chemistry andrinsing chemistry menisci may be connected or separated. In oneembodiment, the cleaning chemistries and rinsing chemistry menisci areconnected. The proximity heads (545, 555) are configured to enableconnection between the cleaning chemistry meniscus and rinsing chemistrymeniscus. In this embodiment, the applied cleaning chemistries are usedonce and not reclaimed after the application. In another embodiment, thecleaning chemistries and rinsing chemistry menisci are separate. In thisembodiment, each of the proximity heads (545, 555) is configured suchthat the cleaning chemistry meniscus is kept distinct from the rinsingchemistry meniscus. Accordingly, in this embodiment, the appliedcleaning chemistry can be reclaimed after application for re-use insubsequent cleaning operations.

Each of the first and second proximity heads, 545, 555, is furtherconfigured to provide a drying operation to dry the surface of thesubstrate after the cleaning and rinsing operations, in one embodimentof the invention. The drying operation may include application of adrying chemistry, such as isopropyl alcohol (IPA) vapor, to thesubstrate surface. In one embodiment, the drying operation is optionalafter the first cleaning and rinsing operation. In the embodiment, wherethe drying operation is not performed after the application of the firstcleaning chemistry and rinsing chemistry, a film of de-ionized water(DIW) is left on the surface of the substrate so as to prevent prematuredrying and/or further contamination. The drying operation is, however,included after the second cleaning and rinsing operation.

During the cleaning process, the substrate is made to move radiallyunder the proximity heads (545, 555), to ensure even application ofvarious chemistries to all portions of the substrate surface. In thisembodiment, the size of the proximity heads is smaller than the width ofthe substrate. The speed of rotation of the substrate underneath theproximity heads is adjusted based on desired exposure time and thetarget removal rate of the polymer residue.

In another embodiment, the proximity heads are configured to have a headthat is slightly larger than the diameter of the substrate so as toprovide a more localized application of the cleaning chemistries withshort exposure time. In this embodiment, the substrate is movinglinearly under the proximity heads.

The short exposure time using proximity heads allows use of concentratedand aggressive chemistries in the cleaning process. The high flowconditions of the aggressive chemistries and the subsequent displacementwith rinsing chemistries enables faster reaction with the polymerresidue contaminants and faster suspension of the reaction therebyenabling optimal removal of the polymer residue contaminants whileminimizing the exposure of the features to the aggressive chemistriesthereby preventing pullback and undercut of fabrication layers of thefeatures, such as the gate structures during the cleaning process. Thus,for instance, APM can be used to remove metal polymer residues around ametal gate structure where tungsten/tungsten compound is used. Eventhough APM is known to dissolve tungsten very quickly, the controlledexposure time enables efficient removal of polymer residue whilepreserving the features around which the polymer residues are formed.FIGS. 6A, 6B and 7 illustrate charts 1, 2, and 3, respectively,depicting the residue cleaning rate with minimum oxide layer loss. Ascan be seen in FIG. 6A, for instance, the concentration of the APM maybe adjusted to provide an etch rate of about 1 Å/sec to about 10 Å/secwith an optimal etch rate of about 5 Å/sec. The material loss in thegate structure can be between about 5 Å and about 10 Å with about 5second exposure time. The concentration of the APM and the exposure timemay be adjusted to obtain acceptable range of polymer residue removalwhile maintaining low material loss of the gate structure material. Theexposure time can be adjusted using precision controls to fine tune theexposure time to an order of about ±0.1 seconds. For instance, a typicalrange of the composition of APM could be in the order of about 1:1:1 onthe concentrated side to about 1:4:50 on the diluted side with astandard concentration of about 1:4:10. For dHF, the range ofconcentration could be between about 1:10 on the concentrated side toabout 1:1000 for diluted side with a standard concentration of about1:100. The standard exposure time would be about 2 seconds with a rangebetween about 1 second to about 20 second. Depending on the proximityhead size, the speed of the substrate may be adjusted to provide therequired exposure time. The proximity head width could be between about10 mm to about 40 mm and the speed of the substrate could be adjusted tothe required exposure time. FIG. 8 illustrates a graph of the targetexposure time to carrier speed for effective removal of polymer residuecontaminants.

The graph illustrated in FIG. 8 depicts the scanning speed againstexposure time for effective removal of the polymer residue contaminantswith two different proximity head widths. The graph identifies thetarget removal rate of the polymer residue. Based on the desired removalrate, the concentration of the first and second application chemistries,speed of the substrate under the proximity heads and exposure time canbe adjusted. For instance, if it is desired to remove 5 Å of tungstenbased residue, the graph identifies the optimal exposure time and speedof the substrate to achieve that goal.

As mentioned earlier, FIGS. 3D, 3E and 4D illustrate the resultant metalgate structure before and after a cleaning operation is performed, inone embodiment of the invention. As can be seen in FIG. 3D illustrates atypical gate structure with polymer residue contaminants formed aroundthe gate structure. FIG. 3E illustrates the result of a traditionalcleaning operation using aggressive chemistries. The polymer residue ontop of a hardmask layer is stripped with severe erosion of hardmasklayer, thereby exposing the underlying layers. FIG. 4D illustrates theresult after a cleaning operation using the first and second cleaningchemistries of the present invention. The precise delivery andcontrolled exposure of the first and second cleaning chemistries to thesubstrate surface enables efficient removal of the polymer residueformed on top of the hardmask without causing any negative effects onthe hardmask layer. Additionally, the controlled exposure of thecleaning chemistries enables removal of the polymer residue formed onthe sidewalls of the metal gate structure while substantially preservingthe metal layers of the gate structure.

FIG. 9 illustrates the process operations involved in removing polymerresidue from around a metal gate structure during post-etch cleaningoperation, in one embodiment of the invention. The process begins atoperation 910, wherein a plurality of process parameters associated withthe metal gate structure and polymer residue formed around the metalgate structure, are determined. The metal gate structure may be amulti-layer structure formed using various fabrication operations. Theprocess parameters are obtained by analyzing the fabrication layers thatform the gate structure and by analyzing the polymer residue formedaround the gate structure. The process parameters may include type,size, composition, temperature associated with each of the fabricationlayers and of the polymer residue and target removal rate associatedwith the polymer residue to be removed. The process parameters definecharacteristics of each of the fabrication layers that comprise the gatestructure and the polymer residue to be removed.

A first cleaning chemistry and second cleaning chemistry are identifiedbased on the process parameters, as illustrated in operation 920. Thefirst and second cleaning chemistry may be aggressive cleaningchemistries and may include Ammonium peroxide mixture (APM) and diluteHydrofluoric acid (dHF). The examples for first and second cleaningchemistry are exemplary and are not restricted to APM and dHF but mayinclude other aggressive chemistries that are known to dissolve oreffectively react to substantially remove the metal polymer residues.Some of the other aggressive chemistries that may be used as cleaningchemistries may include, for example, a mixture of Hydrofluoric andHydrochloric acids (HF/HCl).

A plurality of application parameters associated with the first andsecond cleaning chemistries are defined based on the plurality ofprocess parameters, as illustrated in operation 930. Some of theapplication parameters associated with each of the first and secondcleaning chemistries may include type, concentration, exposure time,temperature, pressure, and flow rate. In addition, the applicationparameters may include speed of the substrate under a first and a secondset of proximity heads and the width of the meniscus at each proximityhead. The exposure time may be calculated as a function of the speed ofthe substrate and the width of the meniscus at each proximity head. Theapplication parameters are defined based on the target removal rate ofthe polymer residue from around the metal gate structure.

The process concludes with the application of the first and secondcleaning chemistries sequentially in a controlled manner using theapplication parameters, as illustrated in operation 940. The applicationof the first and second cleaning chemistries enables substantial removalof the polymer residue from around the metal gate structure whilesubstantially preserving the structural integrity of the metal gatestructure. The application of the first and second cleaning chemistriesmay be accomplished through a computing system that is communicativelyconnected to the first and second proximity heads. One or more precisioncontrols, available at a chemistry application mechanism communicativelyconnected to the proximity heads, may be manipulated using a software inthe computing system to enable controlled application of the first andsecond cleaning chemistries so as to optimally remove the polymerresidue from around the metal gate structure on the surface of thesubstrate while substantially preserving the structural integrity of theone or more fabrication layers that make up the gate structure. Theapplied cleaning chemistries may be reclaimed so that they can bere-used in subsequent cleaning operations thereby enabling optimal useof the simple but expensive cleaning chemistries. Thus, the variousembodiments of the invention provide ways to remove polymer residuesfrom around metal gate structures while preserving the structuralintegrity of the metal gate structure using aggressive chemistries thatare known to easily dissolve the metal used in the metal gatestructures.

For more information on a substrate supporting device, such as a wafercarrier, reference can be made to U.S. patent application Ser. No.11/743,516, entitled “HYBRID COMPOSITE WAFER CARRIER FOR WET CLEANEQUIPMENT”, filed on May 2, 2007, and assigned to the Assignee of thesubject application and is incorporated herein by reference.

For additional information with respect to the proximity head, referencecan be made to an exemplary proximity head, as described in the U.S.Pat. No. 6,616,772, issued on Sep. 9, 2003 and entitled “METHODS FORWAFER PROXIMITY CLEANING AND DRYING.” This U.S. patent, which isassigned to Lam Research Corporation, the assignee of the subjectapplication, is incorporated herein by reference.

For additional information about menisci, reference can be made to U.S.Pat. No. 6,998,327, issued on Jan. 24, 2005 and entitled “METHODS ANDSYSTEMS FOR PROCESSING A SUBSTRATE USING A DYNAMIC LIQUID MENISCUS,” andU.S. Pat. No. 6,998,326, issued on Jan. 24, 2005 and entitled “PHOBICBARRIER MENISCUS SEPARATION AND CONTAINMENT.” These U.S. patents, whichare assigned to the assignee of the subject application, areincorporated herein by reference in their entirety for all purposes.

For additional information about top and bottom menisci, reference canbe made to the exemplary meniscus, as disclosed in U.S. patentapplication Ser. No. 10/330,843, filed on Dec. 24, 2002 and entitled“MENISCUS, VACUUM, IPA VAPOR, DRYING MANIFOLD.” This U.S. patent, whichis assigned to Lam Research Corporation, the assignee of the subjectapplication, is incorporated herein by reference.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications can be practiced within the scope of theappended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the appended claims.

What is claimed is:
 1. A system for preparing a surface of a substrateby removing post etch polymer residue from etched surfaces that define agate structure formed from at least one layer of tungsten metal,comprising: a first proximity head configured to introduce a firstcleaning chemistry as a first meniscus to a portion of the surface ofthe substrate, when present, the first meniscus is introduced to cover alength that extends to at least a diameter of the substrate and a firstwidth that is less than the diameter of the substrate, when present; asecond proximity head configured to introduce a second cleaningchemistry as a second meniscus to the portion of the surface of thesubstrate, the second meniscus is introduced to cover the length thatextends to at least the diameter of the substrate and a second widththat is less than the diameter of the substrate, when present, the firstand the second cleaning chemistries introduced sequentially; and asubstrate support to receive and transport the substrate, the substratesupport controlled by a motor that is coupled to a computing system toactuate movement of the substrate support, the substrate supportcontrolled to move under the first proximity head at a first linearspeed so as to expose the portion of the surface of the substrate to thefirst cleaning chemistry for a pre-defined exposure time and move underthe second proximity head at a second linear speed.
 2. The system ofclaim 1, wherein one or both of the first and the second proximity headsis further designed to apply a rinsing chemistry to the surface of thesubstrate after the application of the first and/or the second cleaningchemistries to the surface of the substrate.
 3. The system of claim 2,wherein the first and the second proximity heads each are configured toapply the rinsing chemistry and the corresponding first or secondcleaning chemistries as distinct menisci.
 4. The system of claim 2,wherein one of the first proximity head or the second proximity head isfurther designed to perform a drying operation following the rinsingoperation, the drying operation performed at the end of the cleaningprocess.
 5. The system of claim 1, wherein the first linear speed isdifferent from the second linear speed.
 6. The system of claim 1,wherein the first linear speed is same as the second linear speed. 7.The system of claim 1, wherein the pre-defined exposure time is definedas a function of the first linear speed and the first width of the firstmeniscus.
 8. The system of claim 1, wherein the first cleaning chemistryis ammonium peroxide mixture and the second cleaning chemistry isdiluted hydrofluoric acid.
 9. A system for preparing a surface of asubstrate by removing post etch polymer residue from etched surfacesthat define a gate structure formed from at least one layer of tungstenmetal, comprising: a first proximity head configured to introduce afirst cleaning chemistry as a first meniscus to a portion of the surfaceof the substrate, the first meniscus is introduced to cover a lengththat extends to at least a diameter of the substrate and a first widththat is less than the diameter of the substrate, when present; a secondproximity head configured to introduce a second cleaning chemistry as asecond meniscus to the portion of the surface of the substrate, thesecond meniscus is introduced to cover the length that extends to atleast the diameter of the substrate and a second width that is less thanthe diameter of the substrate, when present, the first and the secondcleaning chemistries introduced sequentially; and a substrate support toreceive and transport the substrate, when present, the substrate supportcontrolled by a motor that is coupled to a computing system to actuatemovement of the substrate support, the substrate support controlled tomove under the first proximity head at a first linear speed so as toexpose the portion of the surface of the substrate to the first cleaningchemistry for a first pre-defined exposure time, wherein the firstpre-defined exposure time is defined by the first linear speed and thefirst width of the first meniscus and move under the second proximityhead at a second linear speed so as to expose the portion of the surfaceof the substrate to the second cleaning chemistry for a secondpre-defined exposure time, the second pre-defined exposure time definedby the second linear speed and the second width of the second meniscus.10. The system of claim 9, wherein the first width is different from thesecond width.
 11. The system of claim 9, wherein the first width is sameas the second width.
 12. The system of claim 9, wherein the first linearspeed is different from the second linear speed.
 13. The system of claim9, wherein the first linear speed is same as the second linear speed.14. A system for removing post etch polymer residue from etched surfacesthat define a metal gate structure formed on a surface of a substrate,comprising: a carrier for receiving and transporting the substrate; afirst proximity head configured to introduce a first cleaning chemistryto a portion of the surface of the substrate as a first meniscus; asecond proximity head configured to introduce a second cleaningchemistry to the portion of the surface of the substrate as a secondmeniscus, the first and the second cleaning chemistries introducedsequentially; and a motor for moving the carrier under the first and thesecond proximity heads so as to enable application of the first and thesecond cleaning chemistries to the portion of the surface of thesubstrate, the motor coupled to a computing system to control a linearspeed of the carrier moving under the first proximity head and thesecond proximity head so as to expose the portion of the substrate tothe first and the second cleaning chemistries for an exposure timedefined by the linear speed.
 15. The system of claim 14, wherein thelinear speed of the carrier under the first proximity head is differentfrom the linear speed of the carrier under the second proximity head,wherein the exposure time under the first and the second menisci varyingin accordance with the linear speed of the carrier under the first andthe second menisci.
 16. The system of claim 14, wherein each of thefirst and the second proximity heads is further configured to introducea rinsing chemistry to the portion of the surface of the substrate, therinsing chemistry is applied after the application of the first and thesecond cleaning chemistries.
 17. The system of claim 16, wherein thefirst and the second proximity heads are configured to apply the rinsingchemistry and the corresponding first or second cleaning chemistries asdistinct menisci.
 18. The system of claim 16, wherein one of the firstproximity head or the second proximity head is further configured toperform a drying operation following the rinsing operation, the dryingoperation performed at the end of a cleaning process based on thesequence of application of the first and the second cleaning chemistriesto the surface of the substrate.